my Z had all sorts of problems when i first started it up, first problem was that i was off a tooth on the dizzy (distributor) second was a valve was way too tight, (bent a valve) third was the distributor. my car did the exact same thing the first time i drove it, huge explosion through the carb and very little power, there was no hood on it and it was running open headers, it really lit up the night sky!!! check compression, re-time it, check double and triple check your firing order, make sure you dont have any tight or loose valves. check all your plug wires, use wire seperators, only let the wires intersect perpendicular to one another. look for manifold leaks on the cylinders that are running really hot. check to make sure that all the needles in the carb are clean. make sure your accelerator pumps are squirting evenly (visual check) make sure also that nothing crawled up your exhaust (happens to us all the time) and clogged your mufflers with dog food or insulation. when trouble shooting a problem like this eliminate EVERY possible variable and youll find the solution in no time.